Interlinings are the hidden framework of an item of clothing. They ensure correct fitting and optimum wear comfort. Depending on their use, they aid the processability of the item of clothing, increase its functionality and stabilize it. The use of these functions can be applied not only to items of clothing, but also to technical textile applications such as in the furniture industry, the upholstery industry and the home textiles industry.
Important features of interlinings are softness, resilience, texture, wash and care resistance and sufficient abrasion resistance of the carrier material when in use.
Interlinings can be made of non-woven fabrics, woven fabrics, knitted fabrics or comparable textile fabrics, most of which are also provided with a glue, meaning that the interlining can usually be bonded to a cover material either thermally by means of heat and/or by pressure (fusible interlining). The interlining is therefore laminated on top of a cover material. The aforementioned variety of textile fabrics have different feature profiles depending on the production method thereof. Woven fabrics consist of threads/yarns in the warp and weft direction, knitted fabrics consist of threads/yarns that are connected by means of a stitch weave to form a textile fabric. Non-woven fabrics consist of individual fibers that are plaited so as to form a fibrous web, which are mechanically, chemically or thermally bonded.
In mechanically bonded non-woven fabrics, the fibrous web is strengthened by mechanically intertwining the fibers, either by means of a needle technique or by intertwining by means of water or steam jets. Although needling provides soft products, they have a relatively fragile texture, and therefore this technology could only be used in very specific niches in the field of interlinings. In addition, when mechanically needling the fabric, a weight per unit area of >50 g/m2 is usually advised, which is too heavy for a number of interlining applications.
Non-woven fabrics strengthened by water jets can have a lower weight per unit area, but are generally flat and not very resilient.
In chemically bonded non-woven fabrics, the fibrous web is provided with a binder (e.g. acrylate binder) by means of impregnation, spraying or by any other conventional application methods, and is then condensed. The binder binds the fibers to one another to form a non-woven fabric, but produces a relatively rigid product as a result, since the binder extends so as to be distributed over large parts of the fibrous web and the fibers are continuously bonded to one another, as in a composite material. Variations in the texture or softness can only be compensated for to a limited extent by fiber blends or by the binder selection.
Thermally bonded non-woven fabrics are usually strengthened by a calender or by hot air for use as interlinings. In non-woven interlining fabrics, punctiform calender strengthening has become accepted nowadays as the standard technology. In this case, the fibrous web generally consists of polyester or polyamide fibers specifically developed for this process and is strengthened by means of a calender at temperatures that approximate to the melting point of the fibers, a roll of the calender being provided with dotted engraving. Such dotted engraving consists of 64 dots/cm2, for example, and can have a welding surface of 12%, for example. Without a dot arrangement, the interlining would be strengthened in a planar manner and would have an unsuitably hard texture.
The various methods described above for producing textile fabrics are known and described in technical books and in the patent literature.
The glues that are usually applied to interlinings are often thermally activatable and generally consist of thermoplastic polymers. According to the prior art, the technology for applying these glue coatings to the fibrous fabric is carried out in a separate working step. Powder-dot, paste-printing, double-dot, scatter and hot-melt methods are usually used as glue technology and are described in the patent literature. These days, double-dot coating is considered to be the most efficient with regard to adhering to the cover material even after care treatment and in terms of re-adhesion.
Such a double dot has a two-layered structure. It consists of a bottom and a top dot. The bottom dot penetrates the base material and serves as a barrier layer to prevent the return flow of glue and to anchor the top dot particle. Conventional bottom dots consist, for example, of binder and/or of a thermoplastic polymer, which contributes to the bonding strength during fusing. Depending on the chemical used, in addition to anchoring the top dot in the base material, the bottom dot also acts as a barrier layer for preventing the return flow of glue. The main adhesive component in the two-layered composite is primarily the top dot. This can consist of a thermoplastic material, which is scattered over the bottom dot in the form of a powder. After the scattering process, the excess powder (between the dots of the bottom layer) has to be sucked away again. After the sintering process that follows, the top dot is (thermally) bonded to the bottom dot and can serve as the adhesive to the top dot.
Depending on the intended use of the interlining, a different number of dots are imprinted and/or the amount of glue or the geometry of the pattern of dots varies. A typical number of dots is, for example, cP 110 at a coating of 9 g/m2 or cP 52 at a coating amount of 11 g/m2.
Paste printing is also widely used. In this technology, an aqueous dispersion consisting of thermoplastic polymers, usually in particle form having a particle size of <80 μm, thickeners and solvent aids is produced, and then imprinted onto the substrate by means of rotary screen printing in the form of a paste and in a mostly punctiform manner. The imprinted substrate then has to be subjected to a drying process.
It is know that a wide variety of hot-melt adhesive can be used as the bonding media for heat bonding interlinings or linings.
There is currently a trend to use thin, transparent, flexible or open cover materials in the clothing industry, particularly for women's clothing. In order to support these cover materials, an interlining that is very lightweight and has an open structure is advantageous.
The problem of coating such materials using common aqueous paste systems is that these systems penetrate the base during the coating process and significantly contaminate the production plant in the steps that follow. As a result, not only is the quality of the article considerably impaired, but the production plants have to be stopped far more frequently in order to laboriously clean machine parts.
Furthermore, the penetration means that the glue bottom dot cannot be formed effectively and, after the powder has been scattered (double dot coating), an inhomogeneous, somewhat convex dot is formed. Spreading the dot also causes the bottom dot to be “smeary”, and therefore the powder in the edge regions of the bottom dot and also to some extent in the intermediate spaces cannot be sucked away effectively. In addition to contaminating the plant, this leads to attenuation of the composite following bonding.